Basalt

Physical Properties

Hardness: 6.0; Color: dark grey to black or olive green; Luster: dull to vitreous; Crystal structure: aphanitic (fine-grained); Specific gravity: 2.8 - 3.0

Formation & Geological History

Formed from the rapid cooling of magnesium-rich and iron-rich lava exposed at or very near the Earth's surface. Common in oceanic crust and shield volcanoes.

Uses & Applications

Extensively used in construction, for road base, concrete aggregate, railroad ballast, and as a raw material for stone wool insulation.

Geological Facts

Basalt is the most common rock type in the Earth's crust and also makes up most of the surface of the Moon and Mars.

Field Identification & Locations

Identify by its dark color, heavy weight (relative to size), and very fine-grained texture. Often found in volcanic regions or as rounded river cobbles.

Identified on: 5/4/2026

Mode: Standard